1. Field of the Invention
The present invention relates to an optical transceiver, in particular, the invention related to an optical transceiver providing a flexible printed circuit (FPC) board to electrically connect an optical subassembly with a circuit board.
2. Related Prior Art
Typical optical transceiver provides an optical subassembly (OSA), which installs a semiconductor optical device and a circuit board electrically connected with the OSA. The OSA, by receiving an optical connector that provides an optical fiber therein, optically communicates with the optical fiber by the semiconductor optical device, and the optical device converts thus received optical signal into a corresponding electrical signal, or an externally received electrical signal into the optical signal to be propagated within the optical fiber.
One type of the OSA includes a laser diode (LD) to emit optical signal and a photodiode (PD) to monitor the optical signal from the LD, which is often called as a transmitter optical sub-assembly (TOSA). Another type of the OSA includes a photodiode to receive the optical signal transmitted in the optical fiber and to convert the optical signal into an electrical signal, and a pre-amplifier to amplify the electrical signal, which is often called as a receiver optical sub-assembly (ROSA). The optical transceiver generally comprises these OSAs, the TOSA and the ROSA, the circuit board, a frame for mounting the OSAs and the circuit board, and a cover for enclosing these OSAs, the circuit board and the frame. The electrical connection between the OSAs and the circuit board is generally performed by the FPC board. The United States patent, U.S. Pat. No. 5,295,214 has disclosed an exemplary configuration of the FPC board and the circuit board connected with the FPC board.
FIG. 7 is a perspective view showing another conventional configuration of the FPC board. In this conventional configuration, the FPC board 70 is connected in the top surface thereof with the back surface of the circuit board. The circuit board 83 provides a plurality of pads in the back surface, the surface not illustrated in FIG. 7, while, the FPC board 70 provides pads in the top surface. Thus, the FPC board 70 is connected in the top surface thereof with the back surface of the circuit board 83.
However, the conventional FPC board mentioned above aligns its position by the visual inspection or by using a special tool, which prolongs the alignment and makes it troublesome, finally results in the increase of the process cost. Moreover, the alignment of the FPC board relies on the outer shape of the circuit board and that of the FPC board, which means that various tools are necessary for respective circuit board and the FPC board and makes it complex to control or manage the manufacturing process.
The precise alignment using the special tool and the visual inspection has a substantial subject in addition to the prolonged procedure in the process. That is, a conventional transceiver installs the circuit board with the FPC board within the frame after the connection of two boards. Without careful handling of the assembly of two boards, unexpected stress may be induced in soldered portions of two boards, which may break the soldered portion between two boards by the stress.
Additional member such as resin to reinforce and to cover the soldered portion are often used to relax the stress induced in the soldered portion, or dummy pads, which are electrically connected nowhere, may be provided in adjacent to the practical pads connecting two boards. When the FPC board is bent in advance to the assembly so as to facilitate the assembling process, the alignment between tow boards becomes hard. The process to bring the additional resin requires an auxiliary time to apply and to solidify the resin, which increases the process cost.